William Perlman/The Star-LedgerThe Jets' Jim Leonhard knows that 'White Men Can’t Cover' is an unwritten rule in professional football. 'It doesn't affect me,' Leonhard says.Even now, after a full season watching the Jets’ strong safety intercept passes and run down wide receivers, it happens.

Jim Leonhard will walk into the locker room with his teammates, looking like a lost terrier in a pack of Great Danes, and you almost can read the minds of people who see him.

Hey, who gave Opie the shoulder pads?

The team accountant? Sure. The towel boy? Absolutely. But the “quarterback” of arguably the best secondary in the league, a key to this second-round playoff game against the Chargers?

He is 5-foot-8 and 180 pounds ... maybe. He has a baby face with piercing green eyes and a soup-bowl haircut. Put him next to defensive end Shaun Ellis and he could pass for a tattoo.

And then — we’re being honest? — there is the matter of his overwhelming whiteness.

Leonhard is battling a stereotype every time he steps onto an NFL field. “White Men Can’t Jump” might have been a comedy, but “White Men Can’t Cover” is an unwritten rule in professional football.

“That’s part of it,” Leonhard said. “Look at a guy like Leon Washington. Nobody questions him. Well, we’re the same size. No one says, ‘Leon, I don’t think you’re big enough to play football.’”

He shrugs.

“It doesn’t affect me.”

Not any more it doesn’t, but it did affect his career. He didn’t receive any interest from Division 1 schools and had to walk his way onto Wisconsin, where he became a fixture on the all Big Ten team. He wasn’t drafted in the NFL, signing as a free agent with Buffalo in 2005.

He spent three seasons with the Bills before landing in Baltimore, where he became part of Rex Ryan’s defense. Ryan gets a lot of credit for changing the culture of the Jets, and even more attention for his cocky comments about how far his team can go this winter.

But Ryan doesn’t get as much credit for one of his biggest strengths as a coach: He identifies what players do best and puts them in a role that fits their abilities. Leonhard is the perfect example.

He is the one who puts the Jets in the proper coverages on the field, and he’s rarely wrong. He also has emerged as one of the best blitzers on a defense that has built its success on rushing the quarterback.

“He’s the guy who calls the shots,” linebacker Bart Scott said. “Him being back there makes this entire defense better because he’s able to control the coverages, and that’s not easy to do.”

Leonhard does it well. Cornerback Darrelle Revis gets the attention for shutting down opposing receivers, but he leans on the player he calls “the smartest guy on the field” for guidance.

The smartest, and quite often, the smallest. Leonhard is good-natured when asked about his size. The favorite son of Tony, Wis., has to be, since he’s been dealing with the questions for years.

He was a pretty good baseball player in high school and everyone assumed he’d choose that sport. People were disappointed, even angry, when he decided to play football instead.

Here was an 18-year-old Leonhard chasing his dream, only to have everyone raise an eyebrow.

“I never doubted myself that I should be playing football,” he said. “People get stuck on size and things like that. But once you get on that football field and show them that you know how to play the game the right way and show that you have a lot of heart, it doesn’t matter.”

The key to stopping the Chargers will be covering their tall receivers and future Hall of Fame tight end Antonio Gates. Leonhard was asked about how he deals with bigger receivers more times than he could count this week, which ignored the obvious detail.

Opposing receivers are always bigger.

“If you have good position, it doesn’t matter if you’re 6-3 or 5-3 — you have a chance to make a play,” he said. “I’ve seen a lot of 6-3 safeties get jumped over and look like fools in pass coverage.”

Leonhard has been making people, mostly talent scouts and college coaches, look like fools for years now. He is 27 now, and has come to see the benefits of looking like a sophomore in high school.

“Looking young is starting to be a good thing, right?” he said. “Everyone wants to look young, and now I look like I’m 18.”

He doesn’t look much like a football player. You know who does? Vernon Gholston.

What more does a Jets fan need to know?Steve Politi may be reached at spoliti@starledger.com, or follow him at Twitter.com/NJ_StevePoliti

Steve Politi and Dave Hutchinson discuss the Jets as they prepare for the Chargers